Conveying pulverized material



f Sept. 7, 1948. H. STRUCKMANN CONVEYING PULVERIZED MATERIAL 2 Sheets-Sheet 1 Filed NOV. 16, 1945 INVENTOR.

Sept- 7, 1948- H. STRUCKMANN 2,443,745

CONVEYING PULVERIZED MATERIAL Filed Nov. 16, 1943 2 Sheets-Sheet 2 IN VEN TOR.

Patenied Sept. 7, 1948 CQNVEYING PULVERIZEUMATERIAL Holger Struckmann, Riversidm-Calif;

Application November 16, 1943; Serial N0. 510,555

4 Claims.

This invention relatesto conveying pulverized materialand provides an improved apparatus for this purpose;

Pulverized material which has been aerated. has the propertiesof a fluid and may be pumped through closed'conduits like a fluid. To give the pulverized material this property it must be unif-ormlyvmixed with a small volumeof air.

It has been proposed to aerate pulverized material by projecting jets of compressed air into'a compact mass of the material. This method introduced too much air and fails to achieve uniform aeration.

I have found thatuniforrn aeration of pulverized material may be achieved by allowing air to seep slowly into the material and that this is particularly effective when the pulverized material is 'mechanicallyagitated while the air seeps into it. Asa result of this discovery I have devised a new apparatus for pumping and aerating pul verized material. In the form which I consider most desirable this apparatus consists of a pump having a continuously moving impeller, means for causing air to seep into thepulverized material through a porous medium while the material is in contact with the impeller, and means for forming a seal to prevent blow-back.

A further feature of my invention consists in an improved means for forming a seal against back pressure in a pump provided with a screw impeller. The seal is formed by de-aerating the material at an intermediate part ofthe screw impeller.

A further feature of my invention consists 'in means for maintaining a passage of small crosssection surrounding the impeller always'full of material to insure a-"good seal and also tofe'ed the pulverized material at a uniform rate.

In order that myinvention may clearly be understood; I will describe in detail-the new appa ratus involving my'invention which is shown in the accompanying drawings in which:

Fig. 1 is aside elevation of a screw-impeller pump vertically sectioned on the axis of the impeller;

Figs; 2; 3 and l are transversesections onthe lines 2-2, 3-3, 4-4 of Fig. 1; and

Fi 5 is a sectional side elevation of a'screwimpeller pump like that shown: in Fig; l, and

shows a modification in which: the rear bearing a 2. of the impeller shaft is outside the pump casing. The pump shown in Figs. 1-4 has a screw impeller I0 fixed on a rotary shaft l I and surrounded by a casing I2 which provides a passage ineluding a rectangular hopper l3, a cylindrical neck it, a cylindrical de-aeration chamber IS, a cylindrical heck IS, a rectangular aeration chamber ll'having a discharge orifice I3 connected to a closed conduit is; The impeller shaft has a bearing 20 outside the casing and a hanger bearing'2l in the aeration chamber ll of the casing. The shaft has an enlarged portion 22 within the ole-aeration chamber I5 0f the casing.

' Means are provided for causing air or other asto seep into pulverized materia1 in the hopper Is and in the aeration chamber I! and for Withdrawing air from" the'pulverized material in the tie-aeration chamber iii. For this purpose, part of the fioor'of the chambers I3 and I1 and the entire wall of the-de-aeration chamber 15 are formed of blocks of a porous medium having numerous tortuous minute passages through which air may seep. The porous block 23 forming part of the floor of thehopper -I3 is externally covered by a casing 24 'forming'a chamber into which compressed air may be introduced through a pipe 25. A porous block'Zfi forms the entire floor of the aeration chamber l land is externally cov-- ered by a casing 2'! forming a chamber through which air under pressure may be forced through a pipe 28;

The porous blocks 29 which form the wall of the de-aeration chamber 1'5 have theform, of hollow cylinders coaxial with'the'impeller and are externally-covered by'a casing 30 forminga chamber from whichair-may'be exhausted through pipes 3m, 3Ib,-3l c,- 3ldy3le. The casing 30 is most desirably filled with nodular material 32 to support the blocks-29 and is divided into sections by partitions 33. Substantial clearance is allowed between the blocks 29 and the blade of the impeller.

The porous medium used for the block 26 and the block 23 should have about 50 to minute pores per square inch of surface, and the number of pores 'per' square inch should be uniform throughout the in'ner'surface of the block so that theair will seepthrough the block uniformly. To insure uniform-seepage of the air from the surface of the. block it is" desirable that the passages through the block be such as to offer a substantial resistance to the flow of air. For optimum conditions this resistance should be such that the drop in pressure between the outer and inner surfaces of the block is about equal to th pressure at the inner face of the block. Thus, if the pressure in the aeration 'chamber I! is pounds per square inch, the drop in pressure of the air passing through the block 26 should be about 10 pounds per square inch, so that if the air in the chamber provided by the casing 21 is at a pressure of pounds per square inch the air will seep in evenly through the block and enter the chamber i1 gently.

Any one of a number of known types of porous media may be used, including (1) clean graded sand or similar material bonded together by the fusion of a bonding agent, (2) various dry concrete mixes, and (3) micro-porous porcelains and vitrified clays. Most of the available porous media allow air to pass through them more freely than is desirable in my apparatus but any one of them may be made to have the optimum haracteristics above indicated by partially blocking or plugging their pores, as, for example, by painting their outer surfaces.

The shaft bearing 20 is protected from the pulverized material by a sealing collar 36 fixed on the shaft ii and a porous block 31 fixed to the end of the casing i2 and formed to engage both the outer face and the periphery of the sealing collar. The block 31 may be made of the same porous material as the blocks 26 and 23. The outer face of the block is surrounded by a casing 38 to which air under pressure may be admitted by a pipe 39, so that the air seeping through the porous block prevents the pulverized material from passing around the sealing collar.

In the modification shown in Fig. 5, the rear bearing 2| of the impeller shaft is also placed outside the main casing and is protected from the pulverized material by a collar 38' and porous block 31' like those used to protect the bearing Ell. In this case the discharge orifice I3 is in the top of the aeration chamber ll" instead of in the end of the chamber.

A pressure line 60 from a compressor 6! connects with the pipes 25, 28 and-39 which are provided with suitable control valves. A vacuum line 5.! from a vacuum pump 63 connects with the ipes 3!a .'-iie. Three-way valves M are provided so that any one of these pipes may be disconnected from the vacuum line and connected to the pressure line to clear out the pores of any of the blocks 29 while the pump is in operation.

The operation of the pump shown in Figs. 1-4 is as follows:

lhe screw impeller is rotated slowly, for example at about 100 revolutions per minute. The pulverized material to be conveyed is fed into the hopper I 3 where it comes in contact with the front part of the screw impeller. While it is in contact with this part of the impeller it is aerated by air seeping in through the block 23. The aerated material is carried through the neck M by the impeller and at the end of this neck strikes a passage of smaller cross-section owing to the enlargement 22 of the shaft in the de-aeration chamber I 5. This insures a complete filling of the de-aeration chamber with pulverized material. This results in feeding and transporting the pulverized material at a uniform rate. Any excess of pulverized material which cannot enter the de-aeration chamber is returned to the hopper l3 through a by-pass pipe 34 controlled by a valve 35.

As the pulverized material is moved by the screw conveyor through the de-aeration chamber E5 the air which it contains is sucked out through the porous blocks 29 so that the deaerated material is compacted by the screw to form a seal. The seal is a sort of forward-moving block of material within the flights of the conveyor and a wall of pulverized material sucked and held against the blocks 29. An effective seal is thus provided by the material itself so that a substantial clearance may be allowed between the impeller blade and the blocks 29. This prevents injuring the apparatus by any lumps of hard material which may accidentally be present in the pulverized material. The seal prevents the pressure developed by the pump at its discharge end from causing any back-flow into the hopper.

After the pulverized material passes through the neck is and enters the rectangular aeration chamber l7, it is no longer compacted by the screw but is agitated by the blade of the screw. It is evenly and effectively aerated during such agitation by the air seeping in through the porous block 26, and thus acquires the properties of a fluid so that it flows out through the discharge opening it of the pump and through the conduit is with which the pump is connected.

During the operation, air is supplied to the pressure chambers outside the porous blocks 26, 23 and 3? at a constant rate. If a dense mass of the pulverized material momentarily blocks the flow through any of the pores of any one of the porous blocks, the decreased flow through the block results in building up a higher pressure behind the block which blows out the pores tha have been temporarily obstructed.

What I claim is:

1. Apparatus for conveying pulverized material, comprising a screw impeller; a casing surrounding the screw impeller and providing a feed hopper at the entrance end of the screw conveyor, a porous cylindrical wall surrounding an intermediate part of the screw impeller and a non-cylindrical portion having a porous floor under the rear portion of the screw impeller; means providing a chamber surrounding said cylindrical wall and means for maintaining a partial vacuum in said chamber; and means for providing a chamber under said porous floor and means for maintaining a super-atmospheric pressure in said chamber.

2. Apparatus for conveying pulverized mateial, comprising the combination with a screw impeller, of a porous cylindrical wall surrounding a part of the screw impeller, and means for drawing gets out through said wall to de-aerate the material in contact with a portion of the conveyor to form a seal.

3. Apparatus for conveying pulverized material, comprising a screw impeller, a casing surrounding the impeller and formed to provide a hopper, the impeller and easing cooperating to form a passage extending from the hopper and having a part of relatively small cross-section, means for aerating pulverized material in the hopper, and a feedback conduit extending to the hopper from a point of said passage adjacent to the entrance end of the small cross-section part of the passage.

4. Apparatus for conveying pulverized material, comprising a screw impeller whose shaft has an enlarged portion at an intermediate part of the impeller, a casing surrounding the front part of the impeller and providing a hopper and a neck, a porous cylinder surrounding the enlarged portion of the impeller shaft, means for introducing gas into the hopper to aerate the material therein, means for withdrawing gas through the porous cylinder to de-aerate the material therein, and a feedback conduit extending to the hopper from a pointer the neck near the entrance to the porous cylinder.

HOLGER. STRUCKMANN.

REFERENCES CITED UNITED STATES PATENTS Name Date Detweiler Aug. 28, 1894 Number Number 6 Name Date Dodge Aug. 20, 1895 Stokes Dec. 9, 1913 Quigley Feb. 9, 1915 Kinyon Mar. 12, 1918 Morrison Aug. 24, 1920 Kinyon Sept. 15, 1925 Pontoppidan Feb. 8, 1927 Kinyon July 10, 1928 Lepersonne May 19, 1931 Goebels Aug. 28, 1934 Ihlefeldt Aug. 28, 1934 Nielsen Jan. 14, 1936 Newcomer Dec. 14, 1937 Jewell Dec. 7, 1943 

